Carlos Sainz made the ideal start to his Monaco Grand Prix race weekend, while Max Verstappen has work to do.
The change from hard to medium tyres allowed Sainz to assume top spot in FP1, a position which he never relinquished, boasting a buffer of three-tenths over compatriot Fernando Alonso and six-tenths over Lewis Hamilton in the upgraded Mercedes W14 hitting the track for the first time.
Verstappen's session would see him plagued by bottoming issues in the RB19, while there were shunts for Nico Hulkenberg and Alex Albon.
Verstappen did not have the happiest of starts to his race weekend, a "clutch" concern followed by complaints that the "car is bottoming too much".
Ferrari meanwhile were setting the pace, Charles Leclerc and Carlos Sainz swapping P1 times, all while Verstappen continued to complain about the bottoming which had now progressed to "severe".
Leclerc and Mercedes' George Russell soon joined him in car complaints, Russell going into further detail with his concerns over front end stability, while Leclerc did not spill the beans beyond "some changes" being required.
There were also issues for Logan Sargeant who heard a "weird sound" and was forced to coast his Williams back to the pits, while Hulkenberg triggered the red flags after spinning his Haas and whacking the wall at the Nouvelle Chicane.
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While all of that had been happening, Hamilton had worked his way up to P1 in the upgraded Mercedes W14, though the switch from hard to medium tyres saw Sainz reclaim P1 with a 1:13.690, Alonso slotting in three-tenths behind and Hamilton now 0.663s down on that medium compound.
The Red Bull crew had gone to work on Verstappen's RB19 during the earlier red flag delay, though he was not able to rise higher than P6, leaving the Championship leader with work to do.
The Williams mechanics will also have a very short lunch break, as it turned out Sargeant's issues were to be the minor concern of their session, Albon clattering the wall coming out of Sainte Devote to bring the session to an early end.
FP1 times
1 Carlos SAINZ Ferrari 1:13.372
2 Fernando ALONSO Aston Martin +0.338
3 Lewis HAMILTON Mercedes +0.663
4 Sergio PEREZ Red Bull Racing +0.666
5 Charles LECLERC Ferrari +0.721
6 Max VERSTAPPEN Red Bull Racing +0.872
7 Lando NORRIS McLaren +1.095
8 Esteban OCON Alpine +1.213
9 Lance STROLL Aston Martin +1.281
10 Alexander ALBON Williams +1.294
11 Valtteri BOTTAS Alfa Romeo +1.346
12 Kevin MAGNUSSEN Haas F1 Team +1.353
13 Yuki TSUNODA AlphaTauri +1.448
14 Pierre GASLY Alpine +1.494
15 George RUSSELL Mercedes +1.694
16 Nyck DE VRIES AlphaTauri +1.711
17 Oscar PIASTRI McLaren +1.820
18 Logan SARGEANT Williams +2.185
19 Guanyu ZHOU Alfa Romeo +2.312
20 Nico HULKENBERG Haas F1 Team +2.413